2.1.3 - nucleotides and nucleic acids Flashcards
name the pentose sugar in DNA
deoxyribose
name the pentose sugar in RNA
ribose
describe how polynucleotide strands are formed and broken down
- condensation reactions between nucleotides form strong phosphodiester bonds
- hydrolysis reactions use a molecule of water to break these bonds
- enzymes catalyse these reactions
describe the structure of DNA
- molecule twists to form a double helix of 2 deoxyribose polynucleotide strands
- H- bonds form between complementary base pairs on strands that run antiparallel
name the purine bases and describe their structure
- adenine and guanine
- two ringed structure
name the pyrimidine bases and describe their structure
- thymine, cytosine and uracil
- single ringed structure
name the complementary base pairs in DNA
- A-T = 2 hydrogen bonds
- C-G = 3 hydrogen bonds
name the complementary base pairs in RNA
- A-U = 2 hydrogen bonds
- C-G = 3 hydrogen bonds
why is DNA replication described as semi conservative?
new DNA molecule contains one old strand and one new strand
explain the role of DNA helicase in semiconservative replication
breaks hydrogen bonds between base pairs to form 2 single strands, each of which can be used as a ‘template’
how is a new strand formed during semiconservative replication?
1 - free nucleotides (from nuclear sap) attach to exposed bases by complementary base pairing
2 - DNA polymerase joins adjacent nucleotides on new strand in a 5’ to 3’ direction via condensation reactions to form phosphodiester bonds
3 - H- bonds reform
what does ATP and ADP stand for?
adenosine triphosphate and adenosine diphosphate
what is the difference in structure between ATP and ADP?
ATP has 3 inorganic phosphate groups whereas ADP has 2
what is a mutation and how does it happen?
- an alteration to the DNA base sequence
- mutations often arise spontaneously during DNA replication
what is a pentose sugar?
a 5 carbon sugar
compare the function of DNA and RNA
DNA holds genetic information and RNA transfers genetic information from DNA to ribosomes
what is a gene?
a section of DNA coding for a single protein (characteristic)
chromosomes are made up of what?
strands of DNA
what are histones?
DNA binding proteins which support the structure of DNA
each gene is located in a particular area on the chromosome, this is called the what?
locus
what is a nucleotide structure?
- the smallest functional unit of DNA
- monomer of nucleic acid
give two examples of nucleic acids
DNA and RNA
different nucleic acids have different ‘_______’
nucleotides
what is ATP?
the energy carrying molecule
name the two bonds in a nucleotide
- glycosidic bond -> join the base and sugar
- ester bond -> join the phosphate and sugar
- both require a condensation reaction to form
describe and explain the steps of DNA extraction
1 - mash/grind sample to break down tissue/cell walls
2 - add detergent to rupture cell surface membranes
3 - add salt to break H- bonds between DNA and water molecules
4 - add protease enzyme to uncoil DNA and break down associated proteins (histone)
5 - use filter paper to filter the mixture into another beaker to remove unwanted parts/fragments
6 - add ice cold ethanol to test tube to precipitate the DNA
7 - collect DNA by spooling
describe and explain the steps of DNA semi conservative replication
1 - helicase (enzyme) breaks hydrogen bonds between the bases to create a ‘replication fork’; this results in the separated strands providing a template for the new strand of DNA
2 - primase (enzyme) starts the process and makes a primer (small piece of RNA) and this marks the construction point for the new strand
3- DNA polymerase binds to the primer
4 - free floating nucleotides bind to complementary bases
5 - lead strand is made continuously
6 - lag strand cannot be made continuously so is made is small fragments known as Okazaki fragments
7 - ligase seals/joins fragments
8 - hydrogen bonds form between the new and old bases on each strand
why is complementary base pairing needed?
- it ensures the same sequence of nucleotides is produced and therefore conserves genetic information
- it prevents the occurence of random, spontaneous mutations
identify features of the genetic code
- universal -> same bases + sequences in (almost) all living organisms
- non-overlapping -> each triplet is only read once
- degenerate -> more than one base triplet code for almost all amino acids (64 possible for 20 AA)
how does a gene determine the sequence of amino acids in a protein?
consists of base triplets that code for specific amino acids
what does transcription produce and where does it occur?
- produces mRNA
- occurs in nucleus
outline the process of transcription
- hydrogen bonds between base pairs are broken by helicase and DNA uncoils creating a replication fork
- one of the DNA strands (antisense) is used as a template by RNA polymerase to make the mRNA molecule
- free nucleotides line up to their complementary base pair and are joined by phosphodiester bonds and thus form a singled stranded molecule of mRNA
- mRNA moves out the nucleus through a pore and attaches to a ribosome in the cytoplasm
what does ‘m’ in mRNA stand for?
messenger
what does the ‘r’ in rRNA stand for?
ribosomal
what does the ‘t’ in tRNA stand for?
transfer
why does mRNA move out of the nucleus instead of DNA?
DNA has a double strand and therefore is too big, whereas (m)RNA is single stranded so can fit through nuclear pores
what is the function of tRNA?
it carries amino acids to the ribosomes
describe the structure of tRNA
- a single polynucleotide chain folded up into a clover shaped molecule
- held in this shape by H bonds between base pairs
- at one end there is a specific sequence of 3 bases called an anticodon
- at the other end there is an amino acid binding site
what is the start codon?
- AUG (in RNA)
- ATG (in DNA)
- ‘Met’ -> methionine
define ‘polypeptide’
a continuous, unbranched chain of amino acids joined by peptide bonds
how does DNA code for proteins?
- 3 nucleotides make up a triplet code
- each triplet codes for a different amino acid
- the sequence of triplets in a section of DNA codes for a polypeptide
what does translation produce and where does it occur?
- produces proteins
- occurs in cytoplasm on ribosomes
outline the process of translation
- mRNA molecule attaches to ribosomes
- molecules of tRNA (from cytoplasm) have triplet of unpaired bases at one end
- start codon (AUG) binds to complimentary anticodon on first tRNA molcule
- second tRNA then brings in next complimentary anticodon
- rRNA forms a peptide bond between the 2 amino acids
- empty tRNA move away, next tRNA moves in and process repeats until stop codon is reached and final polypeptide is formed
what are the 4 protein structures?
- primary
- secondary
- tertiary
- quaternary
the genetic code is ‘universal’ what does this mean?
it is the same in almost all living organisms - the same triplet of bases code for the same amino acid
the genetic code is ‘non-overlapping’ what does this mean?
it is read from a fixed point in groups of three bases, bases are not read more than once
the genetic code is ‘degenerate’ what does this mean?
for almost all amino acids there is more than one base triplet code (64 combinations for only 20 amino acids)
